English: Ellipsocephalus hoffii Schlotheim,1823 - internal molds of fossil trilobites in silty mudshale from the Cambrian of Bohemia.

Trilobites are extinct marine arthropods. They first appear in Lower Cambrian rocks and the entire group went extinct at the end of the Permian. Trilobites had a calcitic exoskeleton and nonmineralizing parts underneath (legs, gills, gut, etc.). The calcite skeleton is most commonly preserved in the fossil record, although soft-part preservation is known in some trilobites (Examples: Burgess Shale and Hunsruck Slate). Trilobites had a head (cephalon), a body of many segments (thorax), and a tail (pygidium). Molts and carcasses usually fell apart quickly - most trilobite fossils are isolated parts of the head (cranidium and free cheeks), individual thoracic segments, or isolated pygidia. The name "trilobite" was introduced in 1771 by Johann Ernst Immanuel Walch and refers to the tripartite division of the trilobite body - it has a central axial lobe that runs longitudinally from the head to the tail, plus two side lobes (pleural lobes).

The Middle Cambrian Jince Formation (pronounced “In-say”) of Bohemia is famous for its fossiliferous intervals that contain well-preserved trilobites. The Jince Formation’s trilobites have been documented in the literature since the 1700s. One of the more common species is Ellipsocephalus hoffii, first described and illustrated in 1823 by Ernst Friedrich Baron von Schlotheim as Trilobites Hoffii. It’s a rather plain-looking trilobite with a moderately effaced cephalon. Complete exoskeletons of this trilobite are abundant in certain intervals of the Jince Fm. The trilobite specimens seen here are preserved as internal molds, often heavily stained with yellowish limonite, in silty mudshale.

Classification: Animalia, Arthropoda, Trilobita, Polymerida, Ellipsocephalidae

Stratigraphy: Ellipsocephalus hoffii zone (= lower Hydrocephalus lyelli zone), upper Jince Formation, upper Middle Cambrian [Note: Hydrocephalus lyelli was considered a subjective junior synonym of Hydrocephalus rotundatus by Kordule (1990)]

Locality: unrecorded locality at or near the town of Jince, Stredocesky Region, Bohemia, Czech Republic

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References cited & sources of additional info.:

Kordule, V. 1990. Rejkocephalus, a new paradoxid genus from the Middle Cambrian of Bohemia (Trilobita). Vestnik Ustredniho Ustavu Geologickeho 65: 55-60, 2 pls.

Schlotheim, E.F. 1823. Nachträge zur Petrefactenkunde, Zweyte Abtheilung. Gotha. 114 pp. 37 pls. [Trilobites Hoffii is described on pp. 30-31, 34, 85 & illustrated on pl. 22, figs. 2a, 2b.]

Šnajdr, M. 1958. Trilobiti českého středního kambria. Rozpravy Ústředního Ústavu Geologického 24. 280 pp. 46 pls. [Ellipsocephalus hoffii is described on pp. 88-92 & illustrated on pl. 7, figs. 1-8, pl. 8, figs. 1-7.]

Šnajdr, M. 1990. Bohemian Trilobites. Prague. Geological Survey. 265 pp. [Ellipsocephalus hoffii is described & illustrated on pp. 88-89]